This invention relates in general to power management controls, and, more particularly, to power management controls for electric water heaters.
Power management control systems generally are designed to regulate the electrical energy consumed by an electric water heater based upon the electrical energy available to that heater. Some products, often termed energy management systems, are used to manage electrical usage over a period of time or to limit the maximum energy used.
For example, a typical residence may have several electrical appliances which consume large amounts of electrical energy. Some examples include refrigerators, freezers, hot water heaters, furnaces, and air conditioners. In an effort to average the electrical power usage for a home, such appliances may be turned off or allowed to operate under the control of an energy management system. Such limitations can average electrical power usage over time or simply limit the usage during certain periods of time.
Energy management systems in use today have become quite sophisticated, using input as diverse as external temperatures, utility rates and electrical power limits to control appliances. In general, most energy management systems are highly flexible and are not dedicated to specific requirements.
Currently, it is necessary to consult building codes to determine the size of the electrical feeder line to supply a residence or other building. Most often, local building codes are derived from the National Electrical Code published by the National Fire Protection Association. That code defines the calculated load of a residence or other dwelling to be a percentage of the nameplate ratings of the permanent appliances plus a volt-ampere rating per square foot of the dwelling.
Historically, homes first used electricity only for lighting and other small appliances. Next, the convenience of electric cooking ranges, ovens, microwave ovens, water heaters, clothes dryers and air conditions led to a large increase in electrical usage in homes. Just recently, homes have begun installing tankless water heaters for the entire residence. Such devices are no longer the small, low power units designed to fit under a sink, but rather, high volume, high power units designed to replace the conventional water tank style heater. As a result of the tankless heater""s design, power requirements have increased six fold or more over the old tank style water heater.
Electrical codes as discussed previously provide specific guidelines for the service rating, i.e. how much power, measured in volt-amperes, that can be supplied by a given size electrical power feeder. For example, a feeder having a service rating of 200 amperes, 240 volts can deliver this power for only intermittent periods of time. Continuous loads are limited to 80% of this maximum rating or 160 amperes.
A typical 2500 square foot residence might have an electric range and oven rated at 50 amperes, a microwave oven at 12 amperes, a dishwasher at 15 amperes, a clothes dryer at 30 amperes, an air conditioner at 50 amperes and an allotment of 3 volt-amperes per square foot or 31 amperes. It is also recognized that not all appliances operate continuously and thus the following formula is commonly used to take the intermittent use into effect.
Specifically, 100% of the first 10 kVA (42 amperes)plus 40% of the remainder of general loads (39 amperes) and 100% of the heating and air conditioning loads (50 amperes). Adding a conventional 20 ampere tank style water heater adds another 8 amperes (40% of 20) thereby bringing the house load to 139 amperes. Thus, using the maximum continuous feeder load of 160 amperes, there are an additional 21 amperes for miscellaneous appliances and uses.
However, if a tankless water heater is used in place of the tank style heater, the load requirements go from 20 amperes to 120 amperes at 240 volts. Using the 40% load calculation, the increase is an additional 40 amperes and now the total power requirements are 179 amperes which exceeds the feeder rating by 19 amperes and now requires an increase in same to accommodate.
However, even worse, the tankless water heater requirement of 120 amperes is two and a half times as large as the previous largest load. As set forth in the National Electrical Code, section 230-42(a),
xe2x80x9cMinimum Size and Rating. (a) General. The ampacity of the service-entrance conductors before the application of any adjustment or correction factors shall not be less than either (1) or (2). Loads shall be determined in accordance with Article 220. Ampacity shall be determined from Section 310-15. The maximum allowable current of busways shall be that value for which the busway has been listed or labeled.
(1) The sum of the noncontinuous loads plus 125 percent of continuous loads
(2) The sum of noncontinuous load plus the continuous load if the service-entrance conductors terminate in an overcurrent device where both the overcurrent device and its assembly are listed for operation at 100 percent of their ratingxe2x80x9d
If the tankless water heater operates simultaneously with the air conditioner and the clothes dryer, the load would exceed the feeder rating of 200 amperes. Such usage would be a common occurrence in many households.
The historical increase in power requirements has resulted in redesign or retrofitting of residences to meet this larger electrical power need. One option has been simply to increase the electrical feeder power available to the residence. However, this option has been very costly in terms of retrofitting new wiring and wiring fixtures to meet this increase.
Another option has been to install an interlock system which senses when one appliance, for example, a tankless hot water heater switches on and turns off another, for example, an air conditioner to meet the new demand. This switching is done very quickly in order to keep the total power used by the home below the electrical service rating. Such interlock systems can be very complex with many appliances controlled thereby.
Other systems are described in U.S. Pat. No. 5,504,306 entitled xe2x80x9cMicroprocessor Controlled Tankless Water Heater Systemxe2x80x9d which issued on Apr. 2, 1996 to Russell et al. which provides an apparatus for controlling a water delivery system utilizing an instant flow tankless water heater which includes a programmable microprocessor with support circuitry to achieve control of the outlet temperature of a varying flow rate and varying inlet temperature stream.
U.S. Pat. No. 5,325,822 entitled xe2x80x9cElectric Modular Tankless Fluids Heaterxe2x80x9d which issued on Jul. 5, 1994 to Fernandez shows a tankless, flow through electric water heater whose housing is designed for modular application, where serially connected modules define the path of the fluid being heated, in this case water, through the heater from inlet to outlet.
U.S. Pat. No. 4,567,350 entitled xe2x80x9cCompact High Flow Rate Electric Instantaneous Water Heaterxe2x80x9d which issued on Jan. 28, 1986 to Todd Jr. discloses a compact, tankless instantaneous type electric water heater for household and commercial use which provides a plurality of individual heating chambers connected in series flow relationship between a cold water inlet and a hot water outlet.
U.S. Pat. No. 5,866,880 entitled xe2x80x9cFluid Heater With Improved Heating Elements Controllerxe2x80x9d which issued on Feb. 2, 1999 to Seitz et al. shows an electrically powered water heater which includes a controller and a plurality of heating elements for substantially instantaneous heating of fluid passing through the heater; water level sensing circuitry, while the heating elements are incrementally energized/de-energized by means of triacs.
None of the references disclose the present invention.
Thus, there is a need for a new system of handling the increased electrical requirements of the home without (1) increasing the amount of electricity fed into the home and (2) without violating relevant building codes.
The present invention meets this need.
It is an object of the present invention to provide a system for managing the power requirements of a residence or other building.
It is a further object of the present invention to manage the power requirements of a residence or other building without increasing the amount of electricity fed into the house and without violating relevant building codes.
Further objects and advantages of the invention will become apparent as the following description proceeds and the features of novelty which characterize this invention will be pointed out with particularity in the specification annexed hereto.